Rebbi says: If one intends to smite this foe and smites a different foe it follows that he should be liable; but if one intends to smite his foe and smites his friend, should he not be exempt? The verse, rather, comes to teach that payment for a wife's injury belongs to the husband, and payment for (the death of) fetuses belongs to the husband.
Rabbi, Rabbi Yehudah Hanasi, Offered an Alternative Reading
Mekhilta Tractate Nezikin 8:3